NASA

During my recent visit to the US, I was lucky enough to spend 2 exciting weeks working at NASA's Kennedy Space Center in their Applied Physics Lab with Dr. Philip Metzger.

Dr. Metzger's previous research into granular materials focused on deriving theoretical probability density distribution functions for highly idealised systems: monodisperse, 2D, frictionless particles in a static packing (i.e. just at the point of being jammed). However, since hardly any granular materials actually fall into this category, Dr. Metzger's overall aim is to extend his theory to frictional, polydisperse systems under strain. To start off this work, I performed discrete element simulations of such systems and analysed the resulting probability distributions. We gained some interesting insights, which will hopefully help Dr. Metzger with extending his theory.

Apart from studying granular materials, I also learnt about some of the quirky and interesting problems the Applied Physics Lab has solved in the past. The first was a problem with the tiles covering the orbiter getting wet if it rained when it landed after re-entry, and the second (still unsolved!) was how to get rid of the vultures that circle over the launch pad during launch.

And last but not least, two memorable experiences: The first was exploring the space shuttle launch facility, including standing in the massive flame trench, marvelling at the tremendous force of rock projectiles that break off the flame trench during launch and are shot away, and climbing up the launch tower to the place where the astronauts climb into the shuttle.

The second was witnessing the "roll-over" of the space shuttle Discovery orbiter: that is, seeing it being moved from the OPF (orbiter processing facility) to the enormous VAB (vehicle assembly building), which was originally built to house the moon rockets and is the second largest building (by volume) in the world. In the VAB, the orbiter will be connected up to its fuel tank and two solid rocket boosters before being wheeled out to the launch pad a few weeks before launch ("roll-out").

Thank you so much to Dr. Philip Metzger for spending two weeks working with us and showing us NASA "behind-the scenes", and to the Applied Physics Lab for hosting us.

Duke University

As well as working at NASA, I was lucky enough to spend 4 days visiting Dr. Robert Behringer's physics lab at the beautiful Duke University in North Carolina.

Dr. Behringer's group at Duke is the arguably the world leader in photoelastic disk experiments: these disks are a special kind of granular material made from a material, which when viewed through circular polarizers, lights up when highly stressed. This allows us to "see" how stresses and forces propagate through a granular material - something you cannot do very easily with typical granular materials (sand, soil, coffee grains), but which is easily done using computer simulations (DEM).

Furthermore, the group made a recent breakthrough whereby individual contact forces between grains can be measured - this will allow us to make a comparison between our DEM code and photoelastic experiments at the most fundamental level previously, such validation has only been done with macroscopic, or averaged, quantities). Hence, the main purpose of the visit to Dr. Behringer's lab was to spend time understanding the experimental apparatus so it can be accurately modelled using DEM. As well as doing this, I met with Dr. Behringer's students and post-docs and learnt a little about their research.

Thank you so much to Dr. Behringer for hosting me, to all of the Behringer group for taking time out of your busy schedules to talk about your work, and a special thank you to Trushant Majmudar for explaining all the intricacies and fine details of your biaxial test apparatus.

Also a big thank you to my supervisor Dr. Antoinette Tordesillas, without whom none of this would have been possible, as well as scholarships I received from the US Army Corps of Engineers, the Department of Mathematics and Statistics, the Particulate Fluids Processing Centre (PFPC) and the Melbourne University Melbourne Abroad Travelling Scholarship (MATS).

Sounds like fun?

The many and varied experiences I had on this trip were in part due to the fact that granular materials research is itself a varied, exciting and cross-disciplinary field. Getting involved with granular materials can take you from the soil in your backyard, to the sand on a beach in the Bahamas, all the way to Lunar and Martian regolith in outer space! And don't think you need a PhD to get involved: our group welcomes undergraduates as well as graduates to take part in original research. If any of this sounds interesting or you'd just like to know more about our research program, contact Dr. Antoinette Tordesillas .